MPEGed
 

MPEGed allows you to easily modify MPEG file properties without re-encoding and without sacrificing quality. Such properties include resolution, framerate, and full screen aspect ratio. The most common issue with recent MPEGs downloaded from the net is that full screen playback is either 'squished' or 'stretched'. By adjusting the aspect ratio to comply with the MPEG resolution it is possible to achieve correct full screen playback. MPEGed even has an auto detect feature which will try its best to determine what aspect ratio should be used.

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